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Study: A third of world's major aquifers threatened

Wed, 06/17/2015 - 07:00

This map shows groundwater storage trends in the world’s 37 largest aquifers, according to a study led by UC Irvine using 2003-2013 satellite data from NASA's GRACE mission. Of the 37 aquifers, the researchers found that 21 are being depleted. Thirteen of the groundwater basins are considered significantly distressed.

Picture Credit:

Ian James

USA Today

Scientists using satellite data have found that a third of the world's largest aquifers — in places ranging from China and India to the United States — are being rapidly depleted and are seriously threatened.

In two new studies, a team of researchers led by hydrologists from the University of California, Irvine assessed the depletion of groundwater on a global scale using readings from NASA satellites. They also concluded that although there is little solid information about how much water remains in aquifers, it's likely much less than previously estimated, leaving big unanswered questions about how soon those reserves of groundwater might run out.

"If we continue to use groundwater the way it's being used, then there's a high chance that it could be depleted to the point that we can no longer use it in my lifetime in certain areas," said Alexandra Richey, the lead author of the studies.

Richey said she was surprised to learn that rudimentary and widely varying estimates, in some cases dating back to the 1960s and '70s, are often the only available guesses of how much groundwater remains in aquifers. She said that lack of hard data makes it crucial for there to be a major effort to explore aquifers and quantify the amounts of water that remain underground.

"There's no way we can keep using these aquifers at the rates that we are without understanding what some of the tipping points are," Richey said in a telephone interview.

The researchers studied changes in the amounts of water in 37 major aquifers around the world between 2003 and 2013. Of those, 21 aquifers have declined, many of them in arid or semi-arid regions.

Thirteen of those declining aquifers — about one-third of the total — were classified as being "highly stressed," "extremely stressed," or "overstressed," with the most severe situations seen in dry areas where little or no water is seeping into the ground to offset the amounts pumped out.

Some of the regions with the most pronounced depletion of groundwater also are major farming areas. The aquifer beneath California's Central Valley, for instance, was labeled as highly stressed.

The researchers found the Arabian Aquifer System, which supplies water to more than 60 million people, to be the most overstressed in the world, followed by the Indus Basin aquifer of northwestern India and Pakistan, and the Murzuk-Djado Basin in northern Africa.

"The red flags are that over half of the world's biggest aquifers are being depleted. They are past sustainability tipping points, and a third of those big aquifers — 13 of those — are seriously distressed," said Jay Famiglietti, a professor of earth system science at UC Irvine who co-authored the studies.

Famiglietti, who is also senior water scientist at NASA's Jet Propulsion Laboratory, said given how quickly human civilization is consuming groundwater, "we need a coordinated global effort to determine how much is left."

"It is crazy and it is unacceptable that we have not done the exploration of the world's major aquifers, including those in the United States, that we absolutely need to do," Famiglietti said. "If they were oil instead of water, they would have been plumbed to their great depths to understand the availability of the resource."

Studying how much water is available underground would involve drilling and other work to quantify the amounts stored in spaces in the rocks and sand. In the United States, Famiglietti said he would like to see Congress give the U.S. Geological Surveymore funding to conduct this sort of exploration work.

The studies, which were published Tuesday by the journal Water Resources Research, expand upon other previous research drawing on data collected by NASA's twin GRACE satellites. The satellites monitor changes in Earth's gravity and act as a "scale in the sky," measuring shifts in the total amounts of water, both above and below ground.

The research team also included scientists at the National Center for Atmospheric Research, National Taiwan University and UC Santa Barbara.

Michael Campana, a professor of hydrogeology and water resources at Oregon State University who was not involved in the study, praised the research and said he hopes it will be a "wake-up call" to convince policymakers it's important to study how much water is stored in aquifers.

He said the study provides "a good summary of our state of the art of global hydrogeology" — and also "the state of our ignorance."

"If you're trying to assess how resilient these systems are, you have to know how much water is in there," Campana said.

Many areas of the world, such as India and the western United States, rely heavily on groundwater pumped from wells.

The study cites an estimate that groundwater is the primary source of water for about 2 billion people. Climate change and growing populations are projected to increase the pressures on groundwater supplies.

Falling water tables lead to problems such as higher electricity costs to run pumps and worsening water quality in the lower levels of many aquifers.

The regions where the researchers found declining groundwater reserves in the United States included the Atlantic and Gulf Coastal Plains Aquifer. In the southern High Plains, however, the Ogallala Aquifer didn't show up as being in decline, even though scientists have estimated that portions of it likely have only a few decades of water left.

"It doesn't show up in that map because we looked at the whole aquifer, and those aquifers are big, and so the hotspots for depletion tend to be smaller than the size of those aquifers," Famiglietti said.

Elsewhere in the world, areas of rapid depletion include the Nubian Aquifer System in northern Africa, the Canning Basin in Australia and the aquifer system of the North China Plain.

Richey said available estimates of how much groundwater remains to be tapped in the North China Plain vary especially widely, from about a decade to thousands of years — exemplifying the lack of data on aquifers in many areas.

"We've known for a while that the rates of use that we're seeing are unsustainable, and I think this is just contributing to that knowledge," Richey said. "I do feel sometimes that my research can be a little depressing, but I'm also really encouraged by it because I know that getting this information out now can hopefully help implement strategies today so that we can make sure we have reliable resources."

Some of those strategies, she said, can include replenishing aquifers when possible, recycling wastewater and adopting water-saving irrigation techniques.

Richey conducted the research during her doctoral studies at UC Irvine and is now moving to Washington State University for a post-doctoral position. She said she hopes the research not only reveals the scale of the problem but also shows that "it's not too late to take management practices that can help offset the depletion rates that we're seeing."